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From: "eggert at cs dot ucla.edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/101912] -Wmaybe-uninitialized false alarm in tzdb localtime.c
Date: Tue, 30 Nov 2021 16:47:54 +0000	[thread overview]
Message-ID: <bug-101912-4-yKkl1oxD7u@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-101912-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101912

--- Comment #4 from eggert at cs dot ucla.edu ---
(In reply to Aldy Hernandez from comment #3)
> >               && !(leapcnt == 0
> >                    || (prevcorr < corr
> >                        ? corr == prevcorr + 1
> >                        : (corr == prevcorr
> >                           || corr == prevcorr - 1)))))
> > 
> 
> I guess the question is whether language rules allow us to read prevcorr
> when leapcnt== 0?

The C language rules do not allow that. When leapcnt is zero, behavior must be
as if the prevcorr expression is not evaluated.

Although the compiler can generate machine code that evaluates prevcorr at the
machine level (so long as the observable behavior is the same, which is the
case as prevcorr is not volatile and no untoward behavior can result from
evaluating the prevcorr expression), it's incorrect if the compiler warns the
programmer that prevcorr is used uninitialized.

  parent reply	other threads:[~2021-11-30 16:47 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-14 19:27 [Bug tree-optimization/101912] New: " eggert at cs dot ucla.edu
2021-08-16 17:07 ` [Bug tree-optimization/101912] " msebor at gcc dot gnu.org
2021-11-30 15:41 ` aldyh at gcc dot gnu.org
2021-11-30 16:02 ` aldyh at gcc dot gnu.org
2021-11-30 16:47 ` eggert at cs dot ucla.edu [this message]
2021-12-01  7:49 ` rguenther at suse dot de
2021-12-01 16:22 ` aldyh at gcc dot gnu.org
2022-12-25  0:06 ` pinskia at gcc dot gnu.org
2022-12-27 12:26 ` marxin at gcc dot gnu.org
2023-01-09 10:02 ` rguenth at gcc dot gnu.org
2023-01-09 11:19 ` cvs-commit at gcc dot gnu.org
2023-01-09 11:20 ` rguenth at gcc dot gnu.org
2023-04-12 13:30 ` sjames at gcc dot gnu.org
2023-04-12 13:31 ` sjames at gcc dot gnu.org
2023-04-26  6:55 ` rguenth at gcc dot gnu.org
2023-07-04  9:19 ` rguenth at gcc dot gnu.org
2023-07-04  9:19 ` rguenth at gcc dot gnu.org

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